Wheel assembly

ABSTRACT

This disclosure relates to a wheel assembly (1) comprising a wheel, the wheel having a hub and a rim concentrically mounted to the hub, a plurality of deformable chambers (6) disposed outwardly of the rim, each chamber extending about a discreet portion of the wheel and containing a transition substance (15), and an actuator (14) configured to transform the transition substance (15) within each chamber (6) between a fluid state in which the deformable chamber (6) can deform into a conformal state as the wheel encounters an obstacle during use, and a rigid state in which the transition substance is rigidified to maintain the deformable chamber (6) in said conformal state to provide increased purchase on said obstacle.

FIELD

The present invention relates to a wheel assembly, for example a wheelassembly for a vehicle.

BACKGROUND

Wheels typically include an inflatable tyre that provides traction andshock absorption through deformation of the tyre casing. The deformationof the tyre casing allows for increased grip on obstacles and surfaces.Some wheels have grousers that can dig into a soft obstacle, or abutagainst a hard one, in order to provide traction for overcoming largerobstacles. Generally, a wheel is only able to overcome an obstaclehaving a height of less than about one third of the diameter of thewheel.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided a wheelassembly comprising a wheel, the wheel having a hub and a rimconcentrically mounted to the hub; a plurality of deformable chambersdisposed outwardly of the rim, each chamber extending about a discreetportion of the wheel and containing a transition substance; and anactuator configured to transform the transition substance within eachchamber between:

-   -   a fluid state in which the deformable chamber can deform into a        conformal state as the wheel encounters an obstacle during use;        and,    -   a rigid state in which the transition substance is rigidified to        maintain the deformable chamber in said conformal state to        provide increased purchase on said obstacle.

The actuator may be configured to selectively operate the transitionsubstance within each deformable chamber independently of the transitionsubstance within any other deformable chamber.

The wheel may further comprise a plurality of supporting fins extendingradially between adjacent deformable chambers.

The wheel may further comprise a compressible layer disposed between thedeformable chamber and the wheel. The compressible layer may comprise apneumatic bladder.

The wheel assembly may further comprise a sensor arranged to detectdeformation of the deformable chamber.

Alternatively or additionally, the wheel assembly may further comprise asensor arranged to detect the presence of an obstacle.

The actuator may be configured to transform the transition substancebetween the fluid state and the rigid state in response to a signalgenerated by the sensor.

In one example, the transition substance may comprise jamming particlesand an interstitial gas. In this example, the actuator may be configuredto evacuate the interstitial gas from the deformable chamber totransform the transition substance from the fluid state to the rigidstate. Optionally, the actuator may be configured to move gas into thedeformable chamber to transform the transition substance from the rigidstate to the fluid state after said obstacle has been overcome. Theactuator may comprise a pump.

Additionally or alternatively, the deformable chamber may comprise aself-inflation mechanism. The self-inflation mechanism may comprise abiasing member.

In another example, the transition substance may comprise a rheologicalsubstance and the actuator may be configured to alter the viscosity ofthe rheological substance. For example, the rheological substance is amagnetorheological fluid and the actuator comprises an electromagnet. Inan alternative example, the rheological substance is anelectrorheological fluid and the actuator is configured to generate anelectric field. In other examples, the rheological substance is anelectrorheological elastomer and the actuator is configured to generatean electric and/or magnetic field. The wheel assembly may furthercomprise a tread disposed outwardly of the deformable chamber to contactthe ground during use of the wheel assembly. The tread may comprise aplurality of grousers.

In some examples, the deformable chamber may be attached to the wheel.

The deformable chamber may comprise a flexible wall defining a closedtube.

In some examples, the wheel is a drive wheel configured to be coupled toa drive motor.

According to a further aspect of the invention, there is also provided avehicle comprising at least one wheel assembly as described above.

According to a further aspect of the invention, there is also provided awheelchair comprising at least one wheel assembly as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described, by way of example only, withreference to the accompanying drawings, in which:

FIG. 1 shows a wheel assembly according to an embodiment of theinvention;

FIGS. 2A to 2E show a chamber of the wheel assembly of FIG. 1 duringuse;

FIGS. 3A to 3C show the wheel assembly of FIG. 1 overcoming an obstacleduring use;

FIG. 4 shows a wheel assembly according to another embodiment of theinvention;

FIG. 5 shows a wheel assembly according to another embodiment of theinvention;

FIG. 6 shows a wheel assembly according to another embodiment of theinvention;

FIG. 7 shows a vehicle that includes the wheel assembly; and,

FIG. 8 shows a wheelchair that includes the wheel assembly.

DETAILED DESCRIPTION

An embodiment of a wheel assembly 1 according to the invention isillustrated by FIG. 1. The wheel assembly 1 comprises a wheel that isformed of a hub 2 and a rim 3 concentrically mounted to the hub 2 by aconnecting wall 4. In the embodiments illustrated by FIGS. 1 to 6, theconnecting wall 4 comprises a number of spokes arranged between the rim3 and the hub 2; however other arrangements are equally feasible, forexample a solid wheel, or a solid wheel in which cuts outs are made inthe connecting wall 4 for lightness. In some examples, the wheel may beformed of a disc.

The illustrated wheel assembly 1 is a drive wheel, meaning that torqueis applied to the wheel assembly 1 to provide a driving force. In thisexample, the axle 5 is a drive axle that is coupled to a motor or otherdrive means. The drive axle can be coupled to the hub 2 in a number ofconventional means, for example a spine or key. However, it will beappreciated that in other examples the wheel may not be a drive wheel,for example the wheel may be a passive trailer wheel or a passivesteering wheel.

It will be appreciated that the wheel assembly 1 described herein may beused in a wide variety of different applications. For example, the wheelassembly 1 can be used on a vehicle. In one example, the wheel assembly1 is used on a wheelchair. In other examples, the wheel assembly 1 isused on a mobility vehicle, for example a mobility scooter. In yetfurther examples the wheel assembly 1 is used on search and rescuevehicles and specialised off-road vehicles. The wheel assembly 1 may beused on remotely controlled or autonomous vehicles, including spaceexploration vehicles or vehicles for exploring hazardous environments.

As illustrated, the wheel assembly of FIG. 1 further comprises fourchambers 6 arranged about the circumference of the rim 3. Each chamber 6is enclosed by a continuous flexible wall 7 that forms a closed endedelongate tube 8. Each tube 8 is arranged about a discrete portion of therim 3 and is closely spaced to an adjacent tube 8 so that the four tubes8 defining the four chambers 6 provide full coverage of the rim 3.

The chambers 6 are coupled to the rim 3 such that torque can betransferred between the rim 3 and the flexible wall 7. For example, itis envisaged that the flexible wall 7 may be adhered, welded orotherwise attached to an outer surface of the rim 3. To further assistthe transfer of torque, supporting fins 9 can optionally be providedbetween adjacent chambers 6. Each fin 9 extends radially outward of therim 3 to provide a surface against which a portion of the flexible wall7 is supported, that is, the portion of wall 7 defining one of thelongitudinal ends of the respective tube 8. Therefore, as the wheel 1 iscaused to rotate, torque is transferred from the hub 2 to each of thesupporting fins 9 and, in turn, to each flexible wall 7 of eachrespective chamber 6.

Each chamber 6 is filled with a transition substance 15 that isconfigured to transform from a fluid state that allows the chamber 6 todeform, and a rigid state that maintains the chamber 6 in its deformedstate. Therefore, during use, as the wheel assembly 1 encounters anobstacle a chamber 6 can be deformed while the transition substance 15is in a fluid state. Then, the transition substance 15 can betransformed to its rigid state to maintain the chamber 6 in its deformedshape. This can provide increased purchase on the obstacle, allowing thewheel assembly 1 to more easily overcome the obstacle.

An actuator 14 is provided to effect transformation of the transitionsubstance 15 between the fluid state and the rigid state, as explainedfurther hereinafter.

In normal use, as the wheel 1 rolls along a flat surface, the transitionsubstance 15 is in the fluid state. This allows the wheel 1 to provide adegree of compliancy over irregularities in the surface by displacementof the flexible wall 7, providing traction and shock absorption.

As illustrated by FIGS. 2A to 2E, the wheel is described overcoming astep 10, such as a kerb. The step 10 has vertical ii and horizontalfaces 12 that are adjoined by an edge 13. The step 10 has a height thatis slightly greater than one half of the diameter of the wheel, meaningthat conventional wheels will struggle to overcome this step 10.

In a first stage of operation of the wheel assembly 1, shown in FIGS. 2Ato 2B, the transition 15 substance is in the fluid state. The wheelassembly 1 rolls up against the step 10 so that the flexible wall 7 ofthe chamber 6 adjacent the step 10 conforms around the edge 13 of thestep 10. As shown in FIG. 2B, in the conformed state the chamber 6 hasdeformed about the edge 13 such that a part of the chamber 6 overliesthe horizontal face 12 of the step. The deformed shape of the chamber 6is referred to as a conformal shape.

In a second stage of operation, shown in FIGS. 2C to 2D, the actuator 14is activated and the transition substance 15 is made rigid so as toprevent further deformation of the flexible wall 7 and maintain thechamber 6 in its conformal shape. The deformed flexible wall 7 theneffectively acts as a grouser, allowing the portion of the flexible wall7 in contact with the horizontal face 12 of the step 10 to providepurchase on the step 10 as the wheel 1 is rotated. The wheel assembly 1may then roll over the edge 13 of the step 10 and onto the horizontalface 12 with reduced risk of slippage.

In a third stage of operation, shown in FIG. 2E, the actuator 14restores the transition substance 15 to its fluid state allowing theflexible wall 7 to take up its natural shape for normal operation.

A first example of the actuator 14 and transition substance 15 will bedescribed with reference to FIGS. 3A to 3C. These FIGS. illustrate onechamber 6 of the wheel assembly 1 described with reference to FIG. 1 toFIG. 2E.

In the embodiment of FIGS. 3A-3C, the transition substance 15 comprisesjamming particles 19 and an interstitial gas 20. This embodiment relieson the principle of jamming transition to effect the change between thefluid state and the rigid state, whereby the interstitial gas 20 isevacuated to lock the jamming particles 19 together in the rigid statewithin the chamber 6.

As shown in FIG. 3A the chamber 6 is filled with interstitial gas 20.Before the wheel assembly 1 encounters an obstacle the compressibilityof the gas 20 and flexibility of the flexible wall 7 allows the chamber6 to conform to the shape of the obstacle. As shown in FIG. 3B, as thechamber 6 comes into contact with the obstacle the flexible wall 7deforms, allowing the chamber 6 to conform to the shape of the obstacle.Then, as shown in FIG. 3C, the gas 20 is evacuated from the chamber 6,which draws the flexible wall 7 around the jamming particles 19 lockingthem together so that the flexible wall 7 is rigidified in the deformedstate and the chamber 6 is maintained in its conformal state. Therigidified chamber 6 provides increased purchase between the wheelassembly 1 and the obstacle, allowing the wheel to overcome the obstacleas described previously.

As illustrated in FIG. 4, the actuator 14 comprises a pump 22 forevacuating the interstitial gas 20 from the chambers 6. A valve 21 isprovided between the pump and each chamber 6. The valve 21 may be openedand closed by the actuator 14. The pump 22 can either be mounted to thewheel 1, as shown, or can be mounted to the vehicle to which the wheel 1is attached.

To evacuate the interstitial gas 20 the pump 22 is operated until thepressure inside the chamber 6 falls below a threshold level which isbelow atmospheric pressure. The valve 21 is then closed and the pressurelevel inside the chamber 6 is maintained. Atmospheric pressure outsidethe chamber 6 presses the flexible wall 7 against the jamming particles19, causing them to interlock so that the flexible wall 7 is rigidified.Ideally the flexible wall 7 has some elasticity to minimise the numberof folds that form in the wall 7 as the volume of the chamber 6 isreduced.

Preferably, the pump 22 may be reversible in order to restore thetransition substance 15 to the fluid state by pumping gas back into thechamber 6. In this case, the valve 21 is opened, the pump 22 isactivated and the chamber 6 is inflated, whereupon the valve 21 is againclosed to maintain the chamber 6 in its inflated state. Alternatively,as illustrated, a reservoir 23 is provided to store gas that has beenremoved from the chamber 6. In this case, the pump 22 is operated todeflate the chamber 6 by pumping gas from the chamber 6 into thereservoir 23, whereupon the valve 21 is closed to both retain the gas inthe reservoir 23 and to maintain the pressure level in the chamber 6. Inorder to restore the transition substance 15 to the fluid state thevalve 21 is opened and the gas moves back into the chamber 6.

In an alternative example, the interstitial gas 20 is evacuated from thechamber 6 as a result of the pressure applied to the chamber 6 duringdeformation and/or due to the elastic tension in the flexible wall 7. Inthese examples, when the valve 21 is opened the volume of the chamber 6is reduced, forcing out the gas 20. The elastic tension of the wall 7compresses together the jamming particles 19 causing them to interlockso that the flexible wall 7 is rigidified. A pump may be provided toinflate the chamber 6 once the obstacle has been overcome.

In a further alternative example, gas 20 can be moved back into thechamber 6 by providing a biasing member that re-inflates the reservoir.For example, the chamber may include an elastic member that iscompressed as the gas 20 is evacuated, and once the valve 21 isre-opened the biasing member urges the flexible wall 7 into its inflatedstate, drawing gas 20 through the valve 21 and into the chamber 6.

In examples, the jamming particles of the transition substance 15 may besmall individual granules or grains made from any type of metallic,polymer, or other material. In some examples, the jamming particles maybe a ground material, for example coffee grounds, ground glass, sand,rice, sawdust, crushed nut shells, oats, cornmeal, salt, seeds. In apreferred example, the jamming particles are small metallic balls, forexample ball bearings. In another preferred example, the jammingparticles are small plastic beads. In a preferred example, theinterstitial gas of the transition substance 15 is air. However, theinterstitial gas may be another gas, for example nitrogen, carbondioxide, or other gas.

In another embodiment of the invention shown in FIG. 5, in which likefeatures retain the same reference numbers, the transition substance 15comprises a magnetorheological fluid and the actuator 14 comprises anelectromagnet 24. The magnetorheological fluid is configured to changeviscosity in response to a magnetic field. The viscosity of the fluid isvariable depending on the strength of the magnetic field applied, withan increase in the magnetic field strength causing a correspondingincrease in viscosity. In order to transform the magnetorheologicalfluid from the fluid state to the rigid state, electric power isprovided to the electromagnet 24 to generate the magnetic field. Theelectric power and the corresponding magnetic field strength are greatenough to ensure that the magnetorheological fluid is effectively rigid,which maintains the flexible wall 7 and chamber 6 in the conformalstate. The fluid state is restored by deactivation of the electromagnet24 and removal of the magnetic field.

The wheel assembly may include one or more electromagnets 24 per chamber6. For example, one, two, three or four electromagnets 24 may berequired for each chamber 6.

The magnetorheological fluid may be substantially incompressible.Therefore, in order for the flexible wall 7 to conform to an objectduring the first stage of operation of the wheel 1, the flexible wall 7is made from a stretchable, elastic material. This ensures that aportion of the flexible wall 7 may conform to the obstacle.

In examples, the magnetorheological fluid of the transition substance 15comprises a carrier oil and magnetic particles suspended in the carrierfluid, such as oil or water. The magnetorheological fluid optionallyfurther includes a surfactant to prevent settling of the magneticparticles within the carrier fluid. Examples of suitable carrier fluidsinclude silicon oils, mineral oils, paraffin oils, silicone copolymers,white oils, hydraulic oils, synthetic hydrocarbon oil, water, esterifiedfatty acid, or ferrofluid. Examples of the magnetic particles mayinclude pure iron, iron alloys (incl. cobalt, vanadium manganese,molybdenum, silicon, nickel), carbonyl iron, atomized iron,water-atomized iron, iron oxides (incl. Fe₂O₃, Fe₃O₄), low carbon steelgrades, silicon steel, nickel, cobalt, ferritic stainless steel,atomized stainless steel, and the like.

In yet another example, similar to the magnetorheological fluid exampleof FIG. 5, the transition substance 15 comprises an electrorheologicalfluid and the actuator 14 is configured to generate an electric field.The viscosity of the electrorheological fluid is increased by applyingan electric filed to the electrorheological fluid. Therefore, theelectrorheological transition substance 15 can be transformed betweenthe fluid state and the rigid state.

Preferably, the electrorheological fluid comprises a suspension of finesemi-conducting particles in an electrically-insulating fluid, forexample silicone oil.

In other examples, the transition substance 15 may comprise anelectrorheological elastomer, and the actuator 14 may be configured togenerate an electric and/or magnetic field that alters the stiffness ofthe electrorheological elastomer. For example, the electrorheologicalelastomer may comprise a flexible silicon or rubber material withmagnetic and/or charged particles distributed through the material. Inthis way, a magnetic and/or electric field can be used to control thestiffness of the electrorheological elastomer.

In preferred examples, the wheel assembly 1 described above withreference to any of FIGS. 1 to 5 further includes a processor configuredto control the actuator 14 to transform the transition substance betweenthe fluid and rigid states. The wheel assembly 1 may also include one ormore sensors. For example, a sensor 16 may be configured to detectdeformation of the chamber 6, such that the processor is able todetermine when to operate actuator 14. In another example, a sensor maybe provided to detect when the wheel assembly 1 is approaching anobstacle, and/or when the wheel assembly 1 is in contact with anobstacle to determine when to operate actuator 14.

A suitable connection 17 is provided to relay signals between the sensor16, processor and actuator 14, for example a controlled area network, 12C or RS232 are all viable options amongst others. For practical purposesthe processor may be located within the hub 2.

In examples where the transition substance 15 comprises jammingparticles and an interstitial gas, as described with reference to FIGS.3A to 3C, the sensor 16 is a pressure sensor 16 configured to measurethe pressure inside the chamber 6. In this way, during the first stageof operation as the flexible wall 7 conforms to the obstacle, thepressure inside the chamber 6 increases and is measured by the sensor16. The pressure sensor 16 thereby generates a signal which varies inproportion to the deformation of the chamber 6. The signal is relayed tothe processor which is configured to activate the actuator 14 when thepressure level increases above a threshold value in order to cause thetransition substance 15 to transform from the fluid state to the rigidstate. As the actuator 14 evacuates the interstitial gas 20 from thechamber 6, the pressure in the chamber 6 drops. When the pressure leveldrops below a threshold value, the processor may then activate thelockable valve 21 to retain the flexible wall 7 in the rigid state.

Such a pressure sensor 16 may also be used with examples where thetransition substance 15 is a rheological fluid, either amagnetorheological fluid or an electrorheological fluid, as describedabove. In these examples, as the chamber 6 is deformed the internalpressure will increase, which can be detected by a pressure sensor 16,and the actuator 14 can transform the transition substance 15 from thefluid to the liquid state once a threshold pressure has been reached.

Alternatively, in an unillustrated example, the sensor 16 may be adeformation sensor that detects the deformation of the chamber 6 of anyof the above-described examples. For example, the sensor may be anoptical sensor, for example a camera, which is positioned on the wheelassembly 1 or vehicle and visually detects engagement between the wheelassembly 1 and obstacles. In other examples, the sensor 16 may be aphysical pressure sensor, for example a piezo electric sensor, arrangedto detect engagement between the wheel assembly 1 and obstacles. Inother examples, the sensor may be a proximity sensor arranged to detectwhen one part of the flexible wall 7 is proximate to another part,thereby determining deformation of the chamber 6. In each case, theprocessor is configured to operate the actuator 14 in dependence on thedetected obstacle or deformation.

In further examples, the wheel assembly may include an angular positionsensor configured to generate a signal indicative of the part of thewheel assembly 1, in particular which chamber 6 on the wheel assembly 1,is in contact with the obstacle. This angular wheel position may be usedby the processor to determine which chamber 6 has been deformed, andtherefore which chamber 6 to transform from the fluid state to the rigidstate. The sensor 16 can also be used to determine when to change thetransition substance 15 from the rigid state to the fluid state after anobstacle has been overcome.

In further examples, the wheel assembly 1 of any of the above-describedexamples may additionally comprise a compressible layer 18 that extendsaround the rim 3. In this embodiment, the chambers 6 are arranged aroundthe compressible layer 18. The compressible layer 18 is preferablyformed from a pneumatic bladder, but could alternatively be acompressible material such as rubber. The compressible layer 18 spacesthe chambers 6 from the rim 3 of the wheel 1. This allows localisedareas of a chamber 6 to be displaced into the compressible layer 18during deformation, and once the transition substance 15 is rigidifiedthe compressible layer 18 will be held in a deformed state. This in turnprovides the flexible wall 7 with a greater range of movement for agiven chamber 6 size, increasing the size of the contact patch betweenthe flexible wall 7 and the obstacle.

As shown in FIGS. 1 to 6, the wheel assembly 1 may further comprise anouter flexible tread 25 that extends around the wheel 1 outward of thechambers 6, so as to be contactable with the ground during use. Theflexibility of the tread 25 allows the tread 25 to conform to the shapeof an obstacle with the chamber 6 underneath. The tread 25 may be madefrom any high friction material and may further comprise a tread patternto assist with water displacement and/or for increased traction on softsurfaces. In a preferred embodiment, the tread 25 is made from asynthetic rubber. In another example, the tread 25 is made from aflexible metal and includes grousers for increasing traction. In anotherembodiment, the tread 25 is a tyre casing that extends around the sidesof the chambers 6 and into contact with the rim 3 to completely enclosethe chambers 6.

The tread 25 may be adhered to the flexible wall 7 of the chambers 6using a suitable adhesive or welding technique. In embodiments where thetread 25 extends into contact with the rim 3, the tread 25 may grip therim 3 by cooperation of flange portions (not shown) on the rim 3 and acorresponding lip on edges of the tread 25.

In the above described embodiments the wheel assembly 1 comprises fourchambers 6. However, the invention is not limited to four chambers 6 andany appropriate number of chambers 6 is envisaged. For example, in asimplified embodiment, a single chamber 6 is provided that extends aboutthe entire rim 3. In other examples, the wheel assembly 1 includes 2chambers, 3 chambers, 5 chambers, 6 chambers or more.

A greater number of chambers 6 might be provided for greater controlover discrete portions of the wheel 1. Therefore, wheels with a largercircumference will include more chambers 6. Increasing the number ofchambers 6 in this way can allow two or more portions of the wheel 1occupied by individual chambers 6 to respond separately to complexobstacles, or when obstacles are immediately adjacent one another, suchas adjacent steps along a flight of stairs. In this instance theflexible wall 7 of one chamber 6 may rigidify about the first step whilethe flexible wall 7 of the adjacent chamber 6 conforms to the secondstep.

Further, a wheel 1 that is wider in an axial direction may have two ormore chambers 6 positioned side by side so as to cover the full width ofthe wheel 1.

FIG. 7 shows a vehicle 26 that includes several of the wheels 1described above. In particular, FIG. 7 illustrates a rover vehicle,which may be remotely controlled or autonomous. The vehicle 26 includesthe wheels 1 in the front and rear, but it will be appreciated that thewheels 1 may be used only on the front, or only on the rear. FIG. 7 alsoillustrates the vehicle 26 climbing a step 10. Such a vehicle 26 may beused in search and rescue, defence applications, or industrialapplications. Alternatively, such a vehicle 26 may be used forexploration.

FIG. 8 shows a wheelchair 27 that includes several of the wheels 1described above. The wheelchair may include a motor for driving at leastone of the wheels 1, for example the rear wheels. The wheelchair 27includes the wheels 1 in the front and rear, but it will be appreciatedthat the wheels 1 may be used only on the front, or only on the rear.FIG. 8 also illustrates the wheelchair 27 climbing a series of steps 28.In addition, the wheels 1 described above may be used on other mobilityvehicles, for example a wheeled-walker or a mobility scooter.

It will be appreciated that the foregoing description is given by way ofexample only and that modifications may be made to the wheel assembly ofthe present invention without departing from the scope of the appendedclaims.

1. A wheel assembly comprising: a wheel, the wheel having a hub and arim concentrically mounted to the hub; a plurality of deformablechambers disposed outwardly of the rim, each chamber extending about adiscreet portion of the wheel and containing a transition substance; andan actuator configured to transform the transition substance within eachchamber between: a fluid state in which the deformable chamber candeform into a conformal state as the wheel encounters an obstacle duringuse; and, a rigid state in which the transition substance is rigidifiedto maintain the deformable chamber in said conformal state to provideincreased purchase on said obstacle.
 2. A wheel assembly according toclaim 1, comprising four deformable chambers.
 3. A wheel assemblyaccording to claim 1, wherein the actuator is configured to selectivelyoperate the transition substance within each deformable chamberindependently of the transition substance within any other deformablechamber.
 4. A wheel assembly according to claim 1, wherein the wheelfurther comprises a plurality of supporting fins extending radiallybetween adjacent deformable chambers.
 5. A wheel assembly according toclaim 1, wherein the wheel further comprises a compressible layerdisposed between the deformable chamber and the rim.
 6. A wheel assemblyaccording to claim 5, wherein the compressible layer comprises apneumatic bladder.
 7. A wheel assembly according to claim 1, furthercomprising a sensor arranged to detect deformation of the deformablechambers.
 8. A wheel assembly according to claim 1, further comprising asensor arranged to detect the presence of an obstacle.
 9. A wheelassembly according to claim 7, wherein the actuator is configured totransform the transition substance between the fluid state and the rigidstate in response to a signal generated by the sensor.
 10. A wheelassembly according to claim 1, wherein the transition substancecomprises jamming particles and an interstitial gas.
 11. A wheelassembly according to claim 10, wherein the actuator is configured toevacuate the interstitial gas from the deformable chamber to transformthe transition substance from the fluid state to the rigid state.
 12. Awheel assembly according to claim 11, wherein the actuator is configuredto move gas into the deformable chamber to transform the transitionsubstance from the rigid state to the fluid state after said obstaclehas been overcome.
 13. A wheel assembly according to claim 10, whereinthe actuator comprises a pump.
 14. A wheel assembly according to claim10, wherein the deformable chamber comprises a self-inflation mechanism.15. A wheel assembly according to claim 14, wherein the self-inflationmechanism comprises a biasing member.
 16. A wheel assembly according toclaim 1, wherein the transition substance comprises a rheologicalsubstance and the actuator is configured to alter the viscosity of therheological substance.
 17. A wheel assembly according to claim 16,wherein the rheological substance is a magnetorheological fluid and theactuator comprises an electromagnet.
 18. A wheel assembly according toclaim 16, wherein the rheological substance is an electrorheologicalfluid and the actuator is configured to generate an electric field. 19.A wheel assembly according to claim 16, wherein the rheologicalsubstance is an electrorheological elastomer and the actuator isconfigured to generate an electric and/or magnetic field.
 20. A wheelassembly according to claim 1, further comprising a tread disposedoutwardly of the deformable chamber to contact the ground during use ofthe wheel assembly.
 21. A wheel assembly according to claim 20, whereinthe tread comprises a plurality of grousers.
 22. A wheel assemblyaccording to claim 1, wherein the deformable chamber is attached to thewheel.
 23. A wheel assembly according to claim 1, wherein the deformablechamber comprises a flexible wall defining a closed tube.
 24. A wheelassembly according to claim 1, wherein the wheel is a drive wheelconfigured to be coupled to a drive motor.
 25. A vehicle comprising atleast one wheel assembly according to claim
 1. 26. A wheelchaircomprising at least one wheel assembly according to claim 1.